Bip39 Standard. The passphrase isn't picked within the predefined list of 2048 words – it can be any word or phrase you end up picking. BIP39 can be a style implementation that lays out how copyright wallets build the set of words (or "mnemonic codes") which make up a mnemonic https://gogogobookmarks.com/story18911793/bip39-wallets-https-linktr-ee-bip39-not-known-facts-about-bip39